[openssl-users] Personal CA: are cert serial numbers critical?
rgm at htt-consult.com
Wed Aug 16 16:52:16 UTC 2017
On 08/16/2017 10:51 AM, Jakob Bohm wrote:
> On 16/08/2017 16:32, Tom Browder wrote:
>> On Wed, Aug 16, 2017 at 08:36 Salz, Rich via openssl-users
>> <openssl-users at openssl.org <mailto:openssl-users at openssl.org>> wrote:
>> ➢ So, in summary, do I need to ensure cert serial numbers are
>> unique for my CA?
>> Why would you not? The specifications require it, but those
>> specifications are for interoperability. If nobody is ever going
>> to see your certs, then who cares what’s in them?
>> Well, I do like to abide by specs, and they will be used in various
>> browsers, so I think I will continue the unique serial numbering.
>> Thanks, Rich.
> Modern browsers increasingly presume that such private CAs behave exactly
> like the public CAs regulated through the CA/Browsers Forum (CAB/F) and
> the per-browser root CA inclusion programs (the administrative processes
> that determine which CAs are listed in browsers by default).
> Among the relevant requirements now needed:
> - Serial numbers are *exactly* 20 bytes (153 to 159 bits) both as
> numbers and as DER-encoded numbers. Note that this is not the
> default in
> the openssl ca program.
> - Serial numbers contain cryptographically strong random bits,
> currently at
> least 64 random bits, though it is best if the entire serial number
> random from the outside. This is not implemented by the openssl ca
> - Certificates are valid for at most 2 years (actually 825 days).
> - SHA-1 (and other weak algorithms such as MD5) are no longer
> permitted and
> is already disappearing from Browser code.
> - RSA shorter than 2048 bits (and other weak settings such as equally
> DSA keys) are no longer permitted and is already disappearing from
How universal is ECDSA p-256 support?
> - If the certificate is issued to an e-mail address, that e-mail
> address must
> also be listed as an rfc822Name in a "Subject Alternative Name"
Which is also a problem in openssl. You have to put the SAN into the
cnf file. There are a number of hacks to do this from the command line.
More information about the openssl-users